A big-screen iPhone 6 should show up next year while the highly anticipated iPad Mini Retina may be delayed until the fourth quarter, according to Citi Research.

In a research note to investors Friday, Citi began by saying that production of the upcoming iPhone 5S "has been delayed by two to four weeks."

The note continued. "And while this does not preclude a September iPhone 5S launch date, we suspect volumes in September may consequently be challenged," Citi's Glen Yeung wrote, citing "our field work in the hardware supply chain."

At the end of the iPhone 5S analysis, Yeung punctuated it with this: "We...expect a 4.8 [inch] screen iPhone 6 to be launched in 1Q14" (the first quarter of 2014).

The iPhone 5 has a 4-inch screen while the Galaxy S4 from Samsung, Apple's biggest rival, sports a 5-inch screen. So, a 4.8-inch iPhone 6 would, theoretically at least, compete with large-screen phones like the S4.

Citi had a lot more to say about future versions of the iPad Mini. Namely, that it expects a $230-$250 iPad Mini followed by the delayed Retina model that's expected to have a pixel density of 2,048x1,536.

Whereas we had been expecting a new iPad 5, iPad Mini 2, and iPad Mini Retina in 2H13 [the second half of 2013], we now believe that iPad Mini Retina has been delayed until late C4Q13 [calendar fourth quarter] or C1Q14. This puts the emphasis on the reduced-price iPad Mini 2 (we expect this to be priced at $230-$250 versus $329 for the current iPad Mini), ostensibly to better compete with the plethora of low-priced competing tablets, but creating some risk to 2H13 iPad revenue estimates in the process.

And Citi had this to say about the iPad 5, the next version of Apple's 9.7-inch tablet.

We continue to expect iPad 5 to sport characteristics similar to iPad Mini (slimmer, lighter), although the prospect of a
higher-end solution (like the MS Surface Pro) seems unlikely given discussions with Intel have not resulted in an Intel design win at 22nm. We note that 3Q13 is expected to be the last quarter of iPad 2 and iPad 4 production.

With respect to the iPad Mini, NPD DisplaySearch said in May that production of the Retina displays for the device should begin by July with production of the tablet itself in the third quarter.

But a report this week from Digitimes claimed that production of the second-generation iPad Mini may be pushed back to November.

Citi also chimed in about Apple's 24th annual developers gathering, the Worldwide Developers Conference, next week.

We suspect any hardware discussions will only center on the upcoming Macbook refresh. Instead, we anticipate some focus on native services from Apple, namely a Spotify-like music streaming and Pandora-like Internet radio service. In addition, extrapolating from comments made by [Apple CEO] Tim Cook in recent public appearances, we expect some indication that Apple will open up their API to developers, allowing outside influence to things like iCloud, Maps, and Siri.